1. Field of The Invention
This invention relates generally to an electronic weight indicator and more particularly to a meter adapted to convert an analog output of a load cell connected to a weighing platform to a digital display which automatically corrects for changes in the meter such as drift and the like after initial calibration.
2. Prior Art
Electronic scales employing a computer which produces a digital display corresponding to the weight on the scale are known and have been described in the prior art. Such scales have the drawback that they drift and product incorrect displays. Efforts to correct the drift have not been entirely successful.
Thus, in U.S. Pat. No. 4,063,604, issued to Rock, a computing scale is described in which any drift is cancelled by increasing or decreasing the net weight reading in small increments during successive counting cycles to maintain an accurate zero reference. Since this tends to correct only one of the causes of drift--others being errors introduced by the circuitry--complete drift compensation is not achieved.
Similarly, U.S. Pat. No. 4,219,089 to Gard and Bryan describe an electronic counting scale employing auto-zero tracking to correct for drift in the circuitry. This is accomplished by determining if the net weight is less than a pre-determined amount and then introducing periodic corrections in accordance with a specific algorithm, to successively reduce the error. The algorithm is designed to be conservative for large noise distributions, but rapid near zero.
In the devices described in the prior art, the performance of the analog and analog-to-digital circuitry is only monitored on an occasional basis and temperature induced drift is not monitored at all.
It is an object of the invention to provide an electronic weight indicator adapted to convert an analog output of a load coupled to a weighing platform into a digital display incorporating a unique drift compensation feature which enables a computer to continually monitor the performance of the analog and A/D circuitry and correct for any changes detected in this circuitry.
Another object of this invention is to provide an electronic weight indicator for converting an analog signal from a load cell to a digital display that automatically compensates for dead load changes.
A further object of this invention is to provide an electronic weight indicator for converting an analog signal from a load cell to a digital display that is easier and simpler to calibrate.
It is another object of this invention to provide an electronic weight indicator which does not normally require recalibration as a result of analog component changes due to repair, replacement, etc.
It is a further object of the invention to provide an electronic weight indicator in which temperature induced drift is very low.
Another object of the invention is to provide an electronic weight indicator for converting an analog signal from a load cell to a digital display which requires an initial calibration during which deadload is automatically adjusted and thereafter automatically corrects for drift.
A still further object of the invention is to provide an electronic weight indicator in which long term calibration drift due to the electronics is negligible.
Yet another object of the invention is to provide an electronic weight indicator employing a computer that can conveniently check the analog and A/D converter circuitry.
Still another object of the invention is to provide an electronic weight indicator employing a computer provided with an algorithm which permits continuous monitoring of the performance of the analog and A/D converter circuitry.
A still further object of the invention is to provide an electronic weight indicator which provides a more accurate display due to a unique drift compensation feature which compensates for changes in the electronic circuitry.
Yet a further object of the invention is to provide an electronic weight indicator in which the displayed weight is independent of all analog and A/D offsets and gains.
These and further objects will appear as the specification progresses.